Nowadays IMS networks are firmly penetrating in the market due to the increasing demand of mobile and fixed multimedia services. IMS networks are implemented on a 3GPP standardized implementation of Session Initiation Protocol (SIP), and runs over standard Internet Protocol (IP) networks, but existing phone systems (both packet-switched and circuit-switched) are supported. IMS networks truly merge the Internet with the world of mobile telephony; it uses mobile technologies to provide ubiquitous access and Internet technologies to provide appealing services.
Leading the services deployed over IMS network is Rich Communication Suite (RCS) which is a service upgrade that marks the transition of messaging and voice capabilities from Circuit Switched technology to an all-IP world. RCS provides a framework for discoverable and interoperable advanced communication services and detailed specifications for a basic set of advanced communication services. Detailed information about the specification can be found at GSMA webpage as a public document.
Main features of RCS are:
                Enhanced Phonebook with service capabilities.        Enhanced Messaging, since RCS enables a large variety of messaging options including chat and messaging history and file transfer.        Enriched Call. Users may share contents during a voice call instead of the traditional “see what I see” capability.        
For RCS, the one mandatory network element is the IMS core system which enables peer-to-peer communication between RCS clients. Other network nodes can be deployed by the Service Provider to provide additional parts of the RCS feature set. For example the ACS node (or AutoConfiguration Server node), which is responsible for both the client configuration and the network provisioning. The client configuration may be based, for example, on an http or https session or both. Said https session includes the configuration xml, with all the relevant information about the IMS connection for registering (such as IPs or urls, connection parameters and protocols, authorization user, password, etc) and service configuration parameters.
Early stage RCS deployments are characterized by a very small “Active/Registered” (A/R) users ratio and, until sufficient penetration of RCS service is achieved, the A/R ratio is likely to be maintained at very low levels. It is estimated that significantly increasing the A/R ratio may still take several years.
On the other hand, in order to increase the RCS penetration, networks need to be dimensioned according to the expected number of registered users, but the small ratio of active/registered users means that the networks are underused. Optimizing properly the dimensioning of the networks is a main issue for telco companies and users which are registered but their profile is non-active means a problem. Every user registered in a IMS network costs a license to be paid by telco companies and high number of non-active users registered in a network costs a lot of money that has to be paid to a third party (the owner of the network) when actually, the users are not using the network at all. Moreover the existence of a big amount of registered non-active users implies an unnecessary signaling overload in the IMS network.